What is and how can I use the bpy.types.UIPopupMenu?
You don't need that class, just call bpy.context.window_manager.popup_menu():

import bpy

# only executed if run in operator context EXEC_*
def main(context):
    for ob in context.scene.objects:
        print(ob)

class SimpleOperator(bpy.types.Operator):
    """Tooltip"""
    bl_idname = "object.simple_operator"
    bl_label = "Simple Object Operator"

    @staticmethod
    def draw_func(self, context):
        layout = self.layout

        col = layout.column()
        split = col.split(percentage=0.15)
        split.label(text="Some")
        split.label(text="layout")

    def invoke(self, context, event):
        wm = context.window_manager
        wm.popup_menu(self.draw_func, title="THE TITLE", icon="INFO")
        return {'RUNNING_MODAL'}

    def execute(self, context):
        main(context)
        return {'FINISHED'}


def register():
    bpy.utils.register_class(SimpleOperator)


def unregister():
    bpy.utils.unregister_class(SimpleOperator)


if __name__ == "__main__":
    register()

    # test call
    bpy.ops.object.simple_operator('INVOKE_DEFAULT')